1. Field of the Invention
This invention relates in general to a method and apparatus for controlling sleep disorder breathing, particularly one utilizing positive air pressure supplied to a person's breathing passages.
2. Description of the Prior Art
The majority of patients diagnosed with sleep disorders in the United States suffer from excessive daytime sleepiness. The leading cause of this symptom is sleep apnea.
Sleep disorder breathing, such as hypopnea, apnea, or other partial pharyngeal closure, is often combined with pharyngeal wall vibration, which may or may not be audible. Sleep apnea is a potentially lethal condition characterized by multiple obstructive, central or mixed apneas occurring during sleep. A characteristic symptom of sleep apnea includes repetitive episodes of pharyngeal wall vibration, often referred to as snoring when audible. The vibration noted with this syndrome is one in which inspiratory vibrations gradually increase when pharyngeal closure or obstruction of the upper airway develops. A loud, choking inspiratory gasp then occurs as a person's respiratory efforts succeed in overcoming the occlusion. The person frequently wakes. In the morning, the aroused person is usually aware of neither the breathing difficulty nor of the numerous accompanying body movements that at times violently disturb his sleep. A diagnostic study is necessary for an adequate description of the person's sleep breathing pattern.
Apneic episodes during sleep are defined as cessations of air flow at nose and mouth lasting 10 seconds or longer and can be readily documented by polysomnographic recordings. Variations in night-to-night frequency of apneic pauses exist in many patients, with increased frequency appearing to follow upper respiratory infections or use of sedating drugs or alcohol.
In obstructive sleep apnea (OSA), breathing passageways are blocked. In central sleep apnea (CSA), the brain has ceased signaling the body to breathe. Obstructive hypopnea is a milder form of obstructive apnea, usually referring to episodes of partial obstruction of the upper airway passages. Central hypopnea is a milder form of central apnea. Excessive pharyngeal wall vibration, without hypopnea or apnea occurrences, can also be a serious problem. Obstructive and central apnea, obstructive and central hypopnea, and pharyngeal wall vibration will be referred to herein as sleep disorder breathing. In the case of central apnea, the passageways are still open. The lungs of the person form a reservoir for air flow even though the person is not breathing.
Treatments available for sleep apnea vary from weight loss to surgical intervention to prosthetic devices. Although weight loss is the most desirable approach, few patients are able to comply with their diets, and very few can afford to continue the exposure to the symptoms of sleep apnea for six months to a year while losing sufficient weight to reduce or cure the condition. Surgical approaches are only effective in about 50% of the cases, are invasive, expensive and may produce undesirable side effects.
The most successful treatment device has been the nasal continuous positive airway ventilator ("CPAP"). CPAP initially used an adapted vacuum sweeper motor to supply air under pressure to a hose. The hose fed a nasal mask attached it to the patient's face. The advantages of the nasal CPAP system are that it produces immediate relief, is non-invasive and can be used while achieving weight loss and thus avoids the need for surgery. The primary problem with nasal CPAP has been compliance. While nearly all of patients are fitted with nasal CPAP as an initial treatment modality, many cease using the system after about six months.
Investigation of the causes for poor compliance among patients has identified three primary factors all relating to patient comfort. The first factor is the lack of perfect fit and discomfort of wearing the nasal mask. The positive pressure of the ventilator flow is often mentioned as the second factor. Some patients experience an uncomfortable and annoying sensation from the forced air stream in their nose and mount. Third, dry mouth and throat are often cited as the source of dissatisfaction with the sleep apnea ventilators.